A safe efficacious vaccine that prevents the spread of human immunodeficiency virus (HIV) will be essential to arresting the spread of the AIDS epidemic. Studies in non-human primates with simian immunodeficiency virus (SIV) and chimeric HIV/SIV virus (SHIV) have demonstrated that live-attenuated nef-deleted viruses are highly effective; however, such vaccines maintain a low level of pathogenicity. We have established a body of Preliminary Results demonstrating that vaccination of cats with a DNA vaccine containing an feline immunodeficiency virus (FIV) provirus encoding a large deletion within the accessory gene vif will induce immunity protective against infection with wild type FIV. Secondly, other recent studies in non-human primates have shown that co-expression of fusion protein interleukin-2/Ig with DNA vaccines expressing SIVmac239 Gag and HIV-1 Env to enhance protection against clinical disease in vaccinated macaques when challenged with pathogenic SHIV-89.6P. Based on these observations, we hypothesize that the efficacy of a vif-deleted FIV proviral DNA vaccine may be enhanced by co-expression of cytokine genes. FIV mutant proviruses expressing cytokines such as feline interferon-gamma, interleukin-2, or granulocyte- macrophage colony stimulating factor (GM-CSF), will be constructed and tested as attenuated virus DNA vaccines in challenge studies in cats. A second vaccine approach will involve co-inoculation of cats with a FIV deltavif proviral DNA vaccine and a mammalian expression vector encoding an cytokine gene. Lastly, a third approach involving a FIVdeltavif DNA vaccine vector that co-expresses an cytokine gene boosted with a killed whole virus vaccine composed of a heterologous FIV isolate will be characterized for its ability to enhance vaccine efficacy. Importantly, the proposed projects in the FIV/cat model will conduct extensive investigations of antiviral immune responses in DNA vaccinated animals. Thus, it may be possible to identify correlates of protective immunity. Accordingly, knowledge gained in this project from this animal model will provide valuable information for evaluation of DNA vaccines for preventing HIV-1 infection and AIDS in humans.